ABSTRACT Thioredoxin family members involved in cellular protein signaling networks provide an important mechanism regulating many aspects of cell function including proliferation and cell survival. Redox signaling involves a protein post translational modification second in importance only to protein phosphorylation. Unlike protein phosphorylation little is known of redox signaling networks in the cell or how they are altered in cancer. The increased expression of one redox signaling protein in particular thioredoxin-1 (Trx-1) has been associated with aggressive tumor growth, decreased apoptotic cell death and decreased patient survival. The hypothesis upon which our studies are based is that redox signaling through thioredoxin family members is an important signaling mechanism that is deranged in cancer and that understanding redox signaling networks in the cancer cell will allow the identification of novel molecular targets for cancer drug discovery and development, and new strategies to treat cancer. We have used Drosophila genetics together with functional genetic siRNA studies in human cancer cells to identify new redox signaling pathways which we will investigate in human cancer cells. We will also investigate the redox regulation of the unfolded protein response (UPR) which is important for maintaining the synthesis of cell survival proteins during stress, including many angiogenic factors important in cancer. We will conduct in vivo antitumor and mechanistic studies of an inhibitor of Trx-1 in colorectal cancer and of a new antitumor inhibitor of thioredoxin reductase we have developed. The overall objective of our studies is to use redox signaling pathways in cancer to identify new molecular targets for cancer drug discovery and development, and to provide new strategies to treat cancer. The work builds upon our past studies of Trx-1 as a cancer drug target which has led to the development of one cancer drug in clinical trial, and seeks to identify new pathways of redox signaling by thioredoxin family members for the identification of molecular targets for cancer drug discovery.